An item that is unbeliveably crap to the rest of the sane population, yet chavs seem to find hugely desireable. Therefore as one chav gets their hands on the 'chavtastic' item it then becomes part of the chav culture. This is because they cannot think for themselves and follow their 'gang' as they skive school to 'chill with da boys 'innit' and sniff pritt stick, and therefore have no capacity to think for themselves but simply follow each other around swearing and spitting for pleasure.

Dear god, did u see him - he was chavtasic - TO THE MAX!,
Those yellow-gold sovereign rings are chavtastic mate,
Boy racers with subs so loud their car shakes streets miles away are chavtastic,
As is listenin to 'fiddy cent'